The use of radiation to treat medical conditions comprises a known area of prior art endeavor. For example, radiation therapy comprises an important component of many treatment plans for reducing or eliminating unwanted tumors. Unfortunately, applied radiation does not inherently discriminate between unwanted areas and adjacent healthy tissues, organs, or the like that are desired or even critical to continued survival of the patient. As a result, radiation is ordinarily applied in a carefully administered manner to at least attempt to restrict the radiation to a given target volume.
Treatment plans typically serve to specify any number of operating parameters as pertain to the administration of such treatment with respect to a given patient. Such treatment plans are often optimized prior to use. (As used herein, “optimization” will be understood to refer to improving upon a candidate treatment plan without necessarily ensuring that the optimized result is, in fact, the singular best solution.) Many optimization approaches use an automated incremental methodology where various optimization results are calculated and tested in turn using a variety of automatically-modified (i.e., “incremented”) treatment plan optimization parameters.
Many treatment plans provide for exposing the target volume to radiation from a number of different angles. Arc therapy, for example, comprises one such approach. In such a case it often becomes useful or necessary to also adjust various mechanical components (such as, for example, multi-leaf collimators) of the treatment system when moving the radiation source with respect to the target volume. A radiation-treatment plan therefore often provides information regarding useful or necessary adjustments to various mechanical components of the treatment system during such a treatment.
Not infrequently one or more of the available angles includes in the beam's-eye view patient structure that should be protected from radiation. When such patient structure partially overlies (in the beam's-eye view) the patient target volume, a tried-and-true approach to planning the treatment session calls for directing no radiation towards the volume target from such angles. Unfortunately, such an approach can result in effectively losing a considerable number of exposure angles and that circumstance, in turn, can undercut the very reason to use an arc-therapy approach for a particular patient in that using only a reduced number of exposure angles inherently increases the amount of radiation being delivered to at least some non-targeted tissue.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.